Prevention and control of struvite and calcium phosphate precipitation by chelating agents

Hen Sabbag, Asher Brenner, Andrey Nikolski, Eitan J.C. Borojovich

    Research output: Contribution to journalArticlepeer-review

    12 Scopus citations

    Abstract

    Abstract: The problems stemming from struvite precipitation on pipe walls, valves, faucets, and propellers in the anaerobic sludge digestion processes of wastewater treatment plants have been extensively reported. In addition to the diverse sources of the struvite-forming ions (Mg2+, (Formula presented.) , and (Formula presented.)) present in its wastewaters, Israel has hard water with characteristic high concentrations of Ca2+ that causes the formation of calcium phosphate on plant equipment. This study focuses on the use of chelating agents to control struvite and calcium phosphate precipitation. The reaction conditions required to prevent the precipitation of either salt by ethylenediaminetetraacetic acid or nitrilotriacetic acid and for the selective precipitation of struvite after calcium chelation are reported. Both chelating agents promoted the chelation in solution of Ca2+ over that of Mg2+. In contrast, for precipitated calcium phosphate and struvite, higher chelating agent concentrations were required to dissolve the former than the latter. The amounts of both chelating agents, added in proper concentrations, were sufficient to bind mainly the Ca2+ ions, thus preventing the precipitation of Ca3(PO4)2 and leaving more phosphate ions available to precipitate Mg2+ ions as struvite. Performed properly, this process will remove Ca2+ and Mg2+ ions from the supernatant. In addition, after separation, the struvite can be collected and used as fertilizer. The potential toxicity of both chelating agents to the biomass was also studied in this work.

    Original languageEnglish
    Pages (from-to)61-69
    Number of pages9
    JournalDesalination and Water Treatment
    Volume55
    Issue number1
    DOIs
    StatePublished - 3 Jul 2015

    Keywords

    • Anaerobic sludge
    • Calcium phosphate
    • Chelating agents
    • Struvite
    • Wastewater

    ASJC Scopus subject areas

    • Water Science and Technology
    • Ocean Engineering
    • Pollution

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